Recently, mobile electronics such as laptop computers or cell phones are more and more sophisticated. Secondary batteries are expected to be used as the power sources for such mobile electronics because of their high energy density and long life.
Currently, widely used power sources for such mobile electronics are lithium ion secondary batteries in which a cathode is made from a lithium-containing transition metal compound and an anode is made from a lithium storage compound such as carbon materials.
The energy density of the lithium ion secondary batteries, however, is reaching to the theoretical limit, and therefore, development of novel secondary batteries that realize higher capacities is demanded. In addition, since lithium ion secondary batteries have a slow electrode reaction, application of a large current significantly lowers the battery performance. Moreover, lithium ion secondary batteries often fall below the expected capacity or output when being downsized, and need to be charged for a long period of time.
In order to solve such problems of secondary batteries, studies and development are actively made on secondary batteries including an organic radical compound (resin) as a reactant or product material of an electrode reaction.
A secondary battery using an organic radical compound as an electrode active material utilizes a redox reaction of radicals for charge and discharge, so that the reaction rate is fast. Accordingly, such a secondary battery has a high power output and is charged in a comparatively short time.
A polymeric compound having a pyrroline nitroxide structure is proposed as a radical compound used in such a secondary battery (see Patent Literatures 1 and 2). They teach that use of such a polymeric compound allows production of a secondary battery having high energy density and a large capacity.